1. Field
The present invention relates to a wireless communication system that provides multi service for transmitting the same data to a plurality of user equipment units, and also relates to a wireless base station, a user equipment and a multi service management equipment that forms the system.
2. Description of the Related Art
Services realized and provided in a mobile communication system heretofore include services for supplying information to an unspecified number of users such as broadcast services and multicast services, in addition to user specific services such as voice communication and packet communication (electronic mail service and Web access service).
Recently, a system taking into account the user individual services and the common data supply services has been similarly examined in a 3G system and an LTE (Long Term Evolution) system regarded as the next generation of mobile communication systems.
As one technique for realizing the multi service supplying the same data to many terminals, a user data synchronization method represented by MBSFN (Multimedia Broadcast multicast service Single Frequency Network) has been proposed. In this proposed method, a predetermined period for synchronization is set in the data transmitted in a plurality of areas to synchronize between the user data transmitted from different wireless base stations in order to maintain continuity of data reception/data synchronization in the user equipment.
Specifically, when a plurality of wireless base stations (eNodeB) form an MBSFN area, the MBMS (Multimedia Broadcast multicast service) data is the data of the multi service and is delivered to user equipment (UEs) according to the following procedures. The MBMS is described in the 3GPP TS 36.300 V8.2.0.
Procedure 1: An MCE (Multi-cell/multicast Coordination Entity), which is a management equipment for managing a multi service, controls a subordinate wireless base station (eNodeB) and a multi service gateway (EMBMS-GW) which is the data source of the multi service so that the same (time/frequency) wireless resources are used within the MBSFN area as for one service. The wireless base station is controlled through an M2 interface and the multi service gateway is controlled through an M3 interface. The M1 interface is an interface between the EMBMS-GW and the eNodeB, the M2 interface is an interface between the MCE and the eNodeB and the M3 interface is an interface between the MCE and the EMBMS-GW.
Procedure 2: According to IP multicast, the MBMS data is delivered from the multi service gateway (EMBMS-GW) to the wireless base stations (eNodeBs) in the MBSFN area through an M1 interface. The SYNC information such as time stamp is set in the delivered MBMS data in order to perform the synchronization among the wireless base stations (eNodeBs) (to synchronize the transmission timing from the eNodeBs).
Procedure 3: The wireless base station (eNodeB) delivers the MBMS data to the user equipments (UEs) according to the specified SYNC information such as the time stamp.
In the mobile communication system, an area structure (service area range of the base station) formed by a wireless base station (eNodeB) is not uniform and obviously the structure changes according to the condition of the base station and the propagation environment. Therefore, in the mobile communication system, the range in which services can be offered is different even among the wireless base stations having the same performance such as transmission power.
It is a rare case that the user equipment can receive a signal in a line of sight channel even when it is a signal received from the same wireless base station (cell). That is the user equipment generally receives diffraction waves, reflection waves, and delayed waves.
Therefore, in the mobile communication system, generally, the user equipment handles the first choice wave (a signal having the highest reception level and a signal arriving fastest) as a main signal.
Specifically, in unicast communication, quality of the currently received signal is reported from the user equipment to the wireless base station. The wireless base station performs a dynamic control of the wireless resources to use according to the quality information reported from the user equipment, thereby improving the receiving quality of the user equipment as necessary.
In the MBSFN, however, there is no scheme to report the receiving quality of an MBMS service from the user equipment to the base station. Therefore, when the quality of the MBMS data received in the user equipment has deteriorated, the wireless base station may not detect this fact.
Since the MBMS service that is poor in receiving quality may not be improved, the required receiving quality of the MBMS service may not be secured in the user equipment.
In ordinary unicast communication, the user equipment reports the receiving quality information such as Channel Quality Indicator (CQI) and the amount of interference to the wireless base station. The wireless base station dynamically controls the wireless resource to be allocated, based on the report from the user equipment, to maintain the receiving quality.
On the other hand, as mentioned above, in the MBSFN area, reporting the receiving quality from the user equipment to the wireless base station is not performed. Therefore, the wireless base station may not improve the defects of deteriorating the receiving quality in the MBMS service even upon detection of the following situations: the case where a delayed wave of the same service (same channel) is received in the MBSFN area; the case where a radio wave that can be an interference is received from a neighboring unicast cell or SC-MBMS (Single-Cell transmission MBMS) cell outside of the MBSFN area; and the case where an interference wave between the MBSFN areas when a plurality of MBSFN areas are formed and each MBSFN area operates asynchronously.
The wireless base stations in the MBSFN area share the same wireless resource for every MBMS service. Therefore, even when a user equipment reports the receiving quality to the wireless base station, the wireless base station which received the report may not control the wireless resource for itself in order to improve the receiving quality. This is also a problem to be solved in order to improve the receiving quality in the MBMS service.
There is a technique for managing receiving quality in the case of transmitting the same data to a plurality of user equipment, in which, for example, a lowest value in the receiving quality of the delivered data is provided and the quality of the delivered data is set according to the device having the lowest receiving quality of the devices which receive data in the quality of the lowest value or higher (for example, refer to Japanese Laid-Open Patent Publication No. 2006-304067).
The above-mentioned conventional technique, however, may not improve the deterioration itself in the receiving quality caused by the delayed wave or the interference wave. Since a plurality of wireless base stations share the wireless resources, there still remains unsettled problems of the MBMS in that the receiving quality may not be controlled for every wireless base station.